Field of the Invention
This invention relates to optically active lactic acid derivatives having two asymmetric centers, liquid crystal compositions containing said optically active lactic acid derivatives and liquid crystal devices thereof.
The technology of liquid crystal displays has been developed rapidly due to the invention of novel nematic liquid crystals, the discovery of their electro-optic effects and the development of their applications in electronic industries such as electronic watch industries and computer display industries. Liquid crystals also have potential use in television displays (HDTV). However, further improvements are desired so as to improve their contrast, view angle and their switching speed.
In 1975, Meyer et. al. found that chiral smectic C phase is ferroelelctric after a series of experiments conducted on p-(decyloxy) benzylidene-amino-2-methylbutyl-cinnamate (R. B. Meyer, L. Liebert, L. Strzelecki and P. Keller, "Ferroelectric Liquid Crystals" J. Physique Lett., 1975, 36, L69). Since then, the development and the application of such smectic phase liquid crystals have become a challenging research field. In 1980, Clark and Lagerwall invented a device employing such liquid crystals, i.e. an SSFLC (surface-stabilized ferroelectric liquid crystal) light valve which is a basic device of new electro-optic technology (N.A. Clark, S.T. Lagerwall, Appl. Phys. Lett., 1980, 36, 899). The unique advantages of ferroelectric liquid crystals in the speed of switching and in optically memorizing characteristics have led such liquid crystals to its importance in flat panel displays.
The ferroelectricity of ferroelectric liquid crystals are mainly contributed by optically active molecular part of the liquid crystals formed by asymmetric synthesis. Ferroelectric liquid crystal displays generally employ a mixture of liquid crystals in which chiral compounds are used as chiral dopant. The chiral dopant may or may not have chiral smectic C phase (W. Kuczynski, H. Stegemeyer, Chem. Phys. Lett., 1980, 70, 123; F. Leenhouts, S. M. Kelly, A. villiger, Displays, 1990, 41). Intrinsically ferroelectric liquid crystal is also one of nonlinear optical materials which are now under intensive study worldwide.
Lactic acid is a commercially available optically active material which consists of easily convertible functional groups, i.e. hydroxy and carboxy groups, which can be easily converted into other molecular structures. In U.S. Pat. Nos. 4,880,560, 4,852,977, 4,812,259 and 4,556,727 discloses optically active lactic acid derivatives and their applications in liquid crystal compositions and devices. The lactic acid derivatives disclosed therein contain only a single asymmetric center. Their performances in displays are still needed to be further improved.